#include <stdio.h>
int main()
{
	float balance=0;
	float q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	scanf("%f", &q);
	balance += q;
	printf("$%.2f\n", balance/12);
	return 0;
}
